Xerographic development system

ABSTRACT

An apparatus for maintaining a substantially uniform distribution of toner particles within the developer flow in a latent electrostatic image development system in which an electrically conductive member positioned adjacent the flow path of the developer material is connected to a source of electrical potential and biased to a polarity opposite from the polarity on the toner particles in the developer flow. The electrically conductive member is moved in a direction generally transverse to the direction of developer flow. Toner particles are attracted to the conductive member from developer material in portions of the developer flow having greater quantities of toner particles dispersed therein and as the conductive member is transported across the developer flow, toner particles are attracted from the conductive member to portions of the developer flow having lesser quantities of toner particles dispersed therein.

United States Patent 1191 Yang 1451 Aug. 13, 1974 XEROGRAPHICDEVELOPMENT SYSTEM Primary Examiner-Robert R. Mackey 75 Inventor: FrankY. Yang, Webster, NY. Aswan Mnstem [73] Assignee: Xerox Corporation,Stamford, [57] ABSTRACT Conn. An apparatus for maintaining asubstantially uniform Flledi NOV-11,1971 distribution of toner particleswithin the developer [21] AWL Na: 197,874 flowin a latent electrostaticimage development sys tem 1n which an electrlcally conductive memberpositioned adjacent the flow path of the developer matel 1 rial isconnected to a source of electrical potential and [51] Int. Cl G03g13/00 bi d t a polarity opposite from the polarity on the Field ofSearch 1 18/621, 623, 627, 637, toner particles in the developer flow.The electrically 117/175, A, 93-42 conductive member is moved in adirection generally transverse to the direction of developer flow. TonerReferences Cited particles are attracted to the conductive member fromUNITED STATES PATENTS developer material in portions of the developerflow 3,357,403 12/1967 Donalies 118/637 having greater quantities oftoner Particles dispersed 3,330,437 4/1968 Swylcr 118/637 therein and asthe Conductive member is transported 3,396,700 8/1968 Donalies 1 18/637across the developer flow, toner particles are attracted 3,575,1394/1971 Nuzum 1 18/637 from the conductive member to portions of thedevel- 3,645,770 2/1972 Flint ll7/l7.5 per flow having lesser quantitiesof toner particles 3,680,779 8/l972 Reilly 239/3 di d h i 3,707,390l2/l972 Sullivan, Jr. l17/l7.5

9 Claims, 3 Drawing Figures PAIENIE mm 31am saw 1 or 2 INVENTOR, FRANKY. YANG ATTORNEY XEROGRAIHIC DEVELOPMENT SYSTEM BACKGROUND OF THEINVENTION This invention relates in general to the development of latentelectrostatic images and more particularly to maintaining asubstantially uniform toner distribution ina developer flow.

In the practice of electrophotography or xerography, a photosensitivesurface such as xerographic plate comprising a layer of photoconductiveinsulating material supported on a conductive backing is uniformlyelectrostatically charged over its surface and then exposed to a lightpattern of the image to be reproduced, thereby discharging thephotoconductor in the illuminated areas. The areas of the layer thatthereafter remain charged thus form an electrostatic latent image inconformity with the configuration of the subject matter to bereproduced.

The latent electrostatic image may then be developed by contacting itwith a finely divided electrostatically attractable material such as aresinous powder. The powder is held in image areas by the electrostaticcharges on the layer. Where the charge is greatest, the greatest amountof material is deposited; and where the charge is least, little, if any,material is deposited. Reversal development techniques familiar to thoseskilled in the art wherein charged areas that remain on the layer afterexposure represent non-image areas, may also be employed to develop thelatent electrostatic image. Thereafter, the developed xerographic powderimage is usually transferred to a support surface, such as a sheet ofcopy paper to which it may be fixed by any suitable means.

A commonly used developing material in electrostatic copying devicesconsists of a pigmented resinous powder referred to hereinafter astoner" and a coarse granular material hereinafter referred to ascarrier." The carrier is removed in the triboelectric series from thetoner so a charge is generated between the powder and carrier uponmutual interaction. Such charge causes the toner to adhere to thecarrier. The carrier, besides providing a charge to the toner, permitsmechanical control so the toner may readily be brought into contact withthe exposed xerographic surface. As noted hereinabove, the tonerparticles are attracted to the electrostatic latent image to produce avisible powder image. The carrier may also take the form of brushlikefibers having properties and functions similar the the granular carriermaterial. Such a brush-like carrier is described, for example, in U.S.Pat. No. 3,25l,706. The brush may also be formed of fibers formed ofmagnetic carrier granules formed into a brush-like formation through theuse of a magnetic field as described, for example, in U.S. Pat. No.2,832,311.

The quality of the developed image may be affected by the ratio of tonerparticles to carrier granules commonly referred to as tonerconcentration. For example, if there is a deficiency of toner, the imageareas will be unable to attract sufficient toner to fully develop theimage resulting in light copies. On the other hand, if there is anexcess amount of toner in a developer material, the image areas becomeoverly dark, with quantities of toner becoming attracted to non-imageareas.

The reason for this phenomenon is the attractive force holding tonerparticles on a carrier granule is reduced as the number of tonerparticles on the particular carrier granule is increased. Conversely, asthe number of toner particles on a carrier granule is decreased, theattractive force holding the particles on the carrier is increased.Therefore, with fewer toner particles on a carrier granule, theparticles will not be readily given up to the electrostatic charge ofthe latent image. In the case of a high number of toner particles on acarrier granule, the force of attraction therebetween is markedlydecreased, often to the point where even residual charges on non-imageareas is sufficient to attract the toner particles.

In the past, efforts have been made to control the amount of tonerdispensed to the developer mixture by various methods and means.Normally, this has been accomplished by adding toner intermittently onthe basis of a timed cycle or by a device which measures either thetoner concentration directly or the density of the developed image.While such systems are generally satisfactory, they do present someobvious shortcomings. In particular, these systems need time to react tolocalized depletion of toner caused by the development of dense imageareas.

For example, an original may have large non-image areas upon which aresolid-area objects to be developed. Obviously, depletion of the tonerparticles from the developer mixture will be localized. Theindiscriminate addition of toner particles to the developer mixture, ashas been the common practice heretofore employed in the art, hassometimes caused the problems hereinabove described.

It has been proposed in the past to use mechanical means, such asaugers, disposed within the developer material sump, to cross mix thedeveloper material in an attempt to obtain uniform toner distribution.Such mechanical means require ample space for its utilization. Inaddition, since it is only the toner that is required to bere-distributed, it is somewhat inefficient to move the entire developermixture in order to obtain optimum toner distribution, since thedeveloper mixture is formed of a relatively small amount of tonerparticles relative to the amount of carrier granules. Furthermore, suchmixing of the toner particles has heretofore been accomplished in thedeveloper housing which is generally remote from the development zone ofthe system. Thus, there is a time lag between the occurrence oflocalized depletion of toner particles at the development zone, and theoccurrence of reuniform toner distribution therein.

SUMMARY OF THE INVENTION It is therefore an object of the invention toimprove development systems employed in xerographic reproducingapparatus.

Another object of this invention is to control the toner distribution ina developer mixture by selfregulating means.

' Another object of this invention is to eliminate development defectscharacterized by localized developer conditions.

A still further object of this invention is to regulate the tonerdistribution of developer in an automatic copying machine so as tomaintain high quality prints on a continuous basis.

It is still a further object of this invention to minimize the requirednumber of parts and to increase the efficiency of obtaining uniformtoner distribution in development zones.

A still further object of this invention is to provide a tonerdistributing device adjacent the development zone of the xerographicapparatus.

These and other objects of the invention are obtained by providing anelectrically conductive member adjacent the flow path of the developermaterial. The member is connected to a source of electrical potentialand is biased to a polarity opposite from the polarity on the tonerparticles in the developer flow. An electric field is thus created whichextends from the electrically conductive member to the developermaterial. The electric field attracts toner particles to the conductivemember from portions of the developer material having greater quantitiesof toner particles dispersed therein. The electrically conductive memberis moved in a direction generally transverse to the direction ofmovement of developer material to transport the toner particlesattracted to the conductive member so they are attracted by portions ofthe developer mixture having lesser quantities of toner particlesdispersed therein.

Other objects of the invention and further features thereof shall becomeapparent to those skilled in the art in view of the following detaileddisclosure and description of a preferred embodiment of the invention,particularly when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic sectional viewof a xerographic reproducing machine embodying the principles of thepresent invention;

FIG. 2 is an enlarged view ofa portion of the machine illustrated inFIG. I; and

FIG. 3 is a frontal elevation view of substantially the enlarged portionofthe xerographic machine illustrated in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings,FIG. 1 shows a typical xerographic machine in which the presentinvention may be employed. As shown therein, a photosensitive member 11is supported on drum 12 which is driven about shaft 14 by a motor (notshown). Member 11 is covered with layer 13 of electrically conductivematerial which, in turn, is covered on its outer surface with layer 15of photoco'nductive insulating material such as vitreous selenium. Anelectrostatic latent image is formed on member II by passing it undercharging station A and exposin station E.

The charging station includes any suitable means for placing a uniformelectrostatic charge on layer 15 such a corona charging device 16.

Exposing station B includes a source of light 17 and lens 18. Anoriginal subject to be reproduced. such as transparency I9, is disposedbetween the light source and lens. Transparency 19 is fed from reel 20through the beam of light generated by source 17 and then rewound onreel 21 after being exposed. The light. transparency and lens, workingon combination. project on the photosensitive member an optical image.the movement of which is synchronized with the movement of the drum. Theprojected optical image causes selective charge dissipation inilluminated areas of layer l5, thus forming an electrostatic latentimage. Other means of forming such images including means for formingimages on ordinary insulating surfaces are known in the art and may beused in lieu of the one shown.

After the charging and exposing steps are completed. the photosensitivemember passes by development station C wherein the latent electrostaticimage is ren dered visible. Station C will be described more fully inconjunction with FIGS. 2 and 3. Following image development, the nextstep in the typical xerographie process is the transfer step which isaccomplished at transfer station D. The image is transferred fromphotosensitive member 111 to a web of paper 22 or the like which is fedbetween guide rolls 23 and 24. Second corona device 27 cffects theelectrostatic transfer of the developed latent image from member 11 toweb 22. Web 22 is fed from reel 25 before transfer and is rcwound onreel 26 after transfer and fusing. Fusing element 28 is positioned toheat the transferred image and thus fix and permanently bond the imageto paper web 22.

Cleaning station E includes a rotary cylindrical brush 29 which contactsthe photosensitive member subsequent to image transfer and removes anyresidual image material from layer 15, thereby readying it for reuse.The above described process and apparatus are familiar to those skilledin the xerographic arts. Any of the many known equivalents of process orapparatus elements may be employed in connection with the presentinvention.

Now referring to FIGS. 2 and 3, the details of the present inventionshall be more fully described. Development station C includes adeveloper housing 30 comprising side walls 36 and 37 (shown in FIG. 3).A developer mixture is contained in the lower portion of housing 30which functions as a sump therefor. The developer material comprises amixture of charged toner particles and oppositely charged carriergranules. The carrier granules, which function to carry the tonerparticles and to generate a triboelectric charge on the toner particles,normally comprise a core. base or interior composed of any solidmaterial which may be of high specific gravity such as glass or steeland nickel beads. covered with or encased in a suitable covering whichimparts the necessary triboelectrie properties to the granular carriermaterial. The triboelectric relationship between the toner particles andgranular carriers depends on the respective relative positions in thetriboelectric series. In triboelectrification theory. materials arearranged in a column in such a way that each material is charged to apositive polarity when contacted with any material below it in theseries and to a negative polarity when contacted with any material aboveit in the series. It is desirable to select the toner particles andgranular carrier materials so their mutual electrification isconsiderable. The degree of such electrification is governed in mostcases by the distance between the positions in the triboelectric series;that is, the greater distance they are removed from one another thegreater the mutual electrification and the closer they are together inthe series the less the mutual electrification. For a better descriptionof how the triboelectric charge is generated on the toner particles,reference may be had to United States Pat. No. 2.6l8.55 l.

Rotatably disposed within housing 30 is developer distributing member31, having vanes 31' extending therefrom. Member 31 rotates about shaft38 which is suitably journaled by bearings 39 in side walls 36 and 37 ofthe housing.

A magnetic brush is disposed in housing 30 above member 31. The magneticbrush includes a stationary magnet 33 and a roller or applicator member32. Roller 32 is rotatably disposed about magnet 33. The magnetic fieldof magnet 33 attracts the magnetically attractable developer mixture toroller 32. The roller thereafter conveys the developer mixture so thatthe toner is attracted by the latent electrostatic image on layer 15.The roller is mounted on shaft 40, which is suitably journaled in walls36 and 37.by bearings 41. Shafts 38 and 40 are connected to a source ofpower (not shown).

In operation, as member 31 rotates, vanes 31 sweep the developerdisposed in the bottom of housing 30 upward, so that the developer isbrought within the magnetic field of magnet 33. The distance betweenmember 31 and roller 32 of the magnetic brush should be limited so as tomaintain the strength of the magnetic field at a sufficient level toattract the developer onto roller 32.

The developer attracted to roller member 32 by magnet 33 adheres theretothe roller rotates. The magnetic carrier-toner mixture orients itselfalong the lines of magnetic force, thereby forming a structure which issimilar to the bristles of a brush. The developer mixture is thusrotated into close proximity with the latent electrostatic image formedon layer of member 11. The latent electrostatic image attracts tonerparticles form the developer mixture, to thereby develop the latentimage. It should be noted, magnet 33 will be oriented so one of itspoles is positioned to influence the developer mixture on roller 32 sothe mixture will be erect when brought into close proximity with thelatent electrostatic image.

As noted hereinbefore, it is of extreme importance that the tonerdistribution within the developer mixture be uniform to obtain copieshaving desired visual characteristics.

A conductive member 34 such as a wire, is provided in the flow path ofthe developer mixture. The member moves transversely to the movement ofthe developer mixture. One end of member 34 is opcratively connected toa coiled spring 43 which is disposed within housing 42. The other end ofmember 34 is looped over a suitable guide 44 and is affixed to one endof a rotatable member or other suitable means 45. Rotatable member 45 isconnected to shaft 38 and will rotate therewith. Member 45 functions asan eccentric to transform the rotational movement of shaft 38 into areciprocal or translational movement for member 34. As member 45rotates, member 34 will move in a reciprocal member through the flowpath of developer mixture. Spring 43 is provided to return member 34 toits initial position and in addition to provide a force to maintainmember 34 in a taut manner.

One end of spring 43 is joined to a shaft 49. Shaft 49 is journaledwithin side walls 48, only one of which is shown in FIG. 3. The oppositeend 50 of spring 43 is rigidly affixed to housing 42. One end of member34 is also joined to shaft 49. As member 34 moves through the flow pathof developer material, spring 43 is compressed. By utilizing the forceproduced by the compression of the spring, member 34 is maintainedsubstantially taut and is returned to its initial position during thecontinued rotation of shaft 38.

Member 34 is connected via brush 46 to a source of electrical potential47. The member is biased to a suitable potential, for example, 500volts. An electric field is thus created about member 34. The source ofelectrical potential should be of the same polarity as the charge on thecarrier material. The potential of a bare carrier granule should begreater than 500 volts for a reason that shall become more apparenthereinafter.

As noted hereinbefore, the attractive force holding toner particles oncarrier granules is proportional to the number of particles on theparticular carrier. Therefore, with fewer toner particles on a carriergranule, these particles will be more strongly attracted thereto andwill not not be readily given up to the electrostatic charge of thelatent image. Conversely, where a high number of toner particles areattracted to a carrier granule, the force of attraction therebetween ismarkedly decreased, often to the point where even residual charges onnon-image areas are sufficient to attract the toner particles.

Member 34 moving within the flow path of the developer mixture willattract toner particles from carrier granules having a high number oftoner particles attached thereto. The particles are attracted from thecarrier granules to member 34 because the attractive force holding thetoner particles on the toner granules is less than the attractive forcebetween the toner particles and the field of the conductive member.Thereafter, when the toner particles are brought into contact withcarrier granules having relatively fewer toner particles attachedthereto, the attractive force between such toner particles and carriergranule is greater than the attractive force between the toner particlesand the field of the conductive member. Uniform toner distributionwithin the developer mixture may be readily achieved.

Member 34 is preferably positioned substantially adjacent to one of thepoles of magnet 33 so the developer particles are erected when broughtinto contact with the conductive member.

By positioning the conductive member close to the development zone of axerographic apparatus, uniform toner distribution may be readilyachieved. Localized toner depletion due to the reproduction ofsolid-area images is readily compensated for without the time lagheretofore encountered.

It should be specifically understood, member 34 may take other formswithout departing from the scope of this invention. For example, member34 may be an endless chain or belt, driven by a plurality of wheels orpulleys. Other arrangements for member 34 that may readily occur to oneskilled in the arts may be also employed.

In a preferred embodiment, the surface area of member 34 may beincreased by providing thereon projections 34'. Other suitable means forincreasing the surface area of member 34 may be substituted in lieu ofprojections 34. By increasing the surface area of conductive member 34,a greater number of toner particles may be attracted thereto for eachpass of the member through the development zone.

While the present invention is carried out in a specific embodiment, itis not intended to be limited thereby but it is intended to be coveredbroadly within the scope of the appended claims.

What is claimed is:

l. A development system for developing latent electrostatic images on aphotosensitive surface comprismg:

a housing including a sump portion containing a quantity of magneticallyattractable developer material comprising carrier granules and tonerparticles triboelectrically attracted to said carrier granules,

a generally cylindrical applicator member supported for rotation withinsaid housing adjacent said photosensitive surface,

magnetic field producing means supported within said applicator member,for supporting quantities of said developer material on the surface ofsaid up plicator member for contact with said photosensitive surface,

a developer distributing member supported for rotation within saidhousing having a plurality of vanes extending therefrom for transportingdeveloper material from said sump portion into operative contact withsaid cylindrical applicator member,

an electrically conductive member disposed adjacent the path of movementof developer material supported on said applicator member,

a source of electrical potential connected to said electricallyconductive member to bias said conductive member to a polarity oppositefrom the polarity of the toner particles in said developer material onsaid applicator member to create an electric field extending from saidelectrically conductive member to the developer material on saidapplicator member, said electric field attracting toner particles tosaid conductive member from said applicator member from portions of saiddeveloper material having greater quantities of toner particlesdispersed therein, and

means for moving said electrically conductive member in a directiongenerally transverse to the direction of movement of said developermaterial on said applicator member to transport toner particles on saidconductive member proximate to portions of developer material on saidapplicator member having lesser quantities of toner particles dispersedtherein to permit an attraction of the transported toner particles fromsaid conductive member to said portions of developer material on saidapplicator member having lesser quantities of toner particles dispersedtherein.

2. The development system in accordance with claim 1 wherein saidconductive member is positioned substantially adjacent one of the polesof said magnetic field producing means.

3. The development system in accordance with claim 2 wherein saidconductive member includes means associated therewith to increase thesurface area thereof.

4. The development system in accordance with claim 1 wherein saidconductive member includes means associated therewith to increase thesurface area thereof.

5. A development system for developing latent electrostatic imagescarried by a photoconductive surface: a sump having developer materialtherein, means including a magnetic transport means for moving saiddeveloper material from said sump along a predetermined path to thephotoconductive surface, said developer material including magneticcarrier granules and toner particles triboelectrically attracted to saidcarrier granules, a member disposed adjacent said magnetic transportmeans, means for reciprocally moving said member in a transversedirection to said predetermined path for moving toner particles fromportions of said developer material on said magnetic transport meanshaving greater quantities of toner particles dispersed therein toportions of developer material on said magnetic transport means havinglesser quantities of toner particles dispersed therein.

6. The structure as recited in claim 5 wherein said magnetic transportmeans is located to present developer to the latent image.

7. In a development system for developing latent electrostatic imagescarried by a photoconductive surface: a sump having developer materialtherein, means including magnetic transport means for moving saiddeveloper material from said sump along a predetermined path to thephotoconductive surface. said developer material including magneticcarrier granules and toner particles triboelectrically attracted to saidcarrier granules, an electrically conductive member. an electricallyconductive member disposed adjacent said magnetic transport means. meansfor moving said conductive member in a transverse direction to saidpredetermined path. a source of electrical potential connected to saidelectrically conductive member to bias said conductive member to apolarity which is the same as the polarity of the electrostatic image,said electrically conductive member being so located relative to saidmagnetic transport means that during movement thereof toner particlesare attracted thereto from portions of developer material on saidmagnetic transport means having a greater quantity of toner particlesdispersed therein for movement to portions of developer material on saidmagnetic transport means having lesser quantities of toner particlesdispersed therein to permit attraction thereto of the toner particles onsaid conductive member.

8. The structure as recited in claim 7 wherein the movement of saidconductive member is reciprocal.

9. The structure as recited in claim 7 wherein said magnetic transportmeans is located to present developer to the latent image.

1. A development system for developing latent electrostatic images on aphotosensitive surface comprising: a housing including a sump portioncontaining a quantity of magnetically attractable developer materialcomprising carrier granules and toner particles triboelectricallyattracted to said carrier granules, a generally cylindrical applicatormember supported for rotation within said housing adjacent saidphotosensitive surface, magnetic field producing means supported withinsaid applicator member, for supporting quantities of said developermaterial on the surface of said applicator member for contact with saidphotosensitive surface, a developer distributing member supported forrotation within said housing having a plurality of vanes extendingtherefrom for transporting developer material from said sump portioninto operative contact with said cylindrical applicator member, anelectrically conductive member disposed adjacent the path of movement ofdeveloper material supported on said applicator member, a source ofelectrical potential connected to said electrically conductive member tobias said conductive member to a polarity opposite from the polarity ofthe toner particles in said developer material on said applicator memberto create an electric field extending from said electrically conductivemember to the developer material on said applicator member, saidelectric field attracting toner particles to said conductive member fromsaid applicator member from portions of said developer material havinggreater quantities of toner particles dispersed therein, and means formoving said electrically conductive member in a direction generallytransverse to the direction of movement of said developer material onsaid applicator member to transport toner particles on said conductivemember proximate to portions of developer material on said applicatormember having lesser quantities of toner particles dispersed therein topermit an attraction of the transported toner particles from saidconductive member to said portions of developer material on saidapplicator member having lesser quantities of toner particles dispersedtherein.
 2. The development system in accordance with claim 1 whereinsaid conductive member is positioned substantially adjacent one of thepoles of said magnetic field producing means.
 3. The development systemin accordance with claim 2 wherein said conductive member includes meanSassociated therewith to increase the surface area thereof.
 4. Thedevelopment system in accordance with claim 1 wherein said conductivemember includes means associated therewith to increase the surface areathereof.
 5. A development system for developing latent electrostaticimages carried by a photoconductive surface: a sump having developermaterial therein, means including a magnetic transport means for movingsaid developer material from said sump along a predetermined path to thephotoconductive surface, said developer material including magneticcarrier granules and toner particles triboelectrically attracted to saidcarrier granules, a member disposed adjacent said magnetic transportmeans, means for reciprocally moving said member in a transversedirection to said predetermined path for moving toner particles fromportions of said developer material on said magnetic transport meanshaving greater quantities of toner particles dispersed therein toportions of developer material on said magnetic transport means havinglesser quantities of toner particles dispersed therein.
 6. The structureas recited in claim 5 wherein said magnetic transport means is locatedto present developer to the latent image.
 7. In a development system fordeveloping latent electrostatic images carried by a photoconductivesurface: a sump having developer material therein, means includingmagnetic transport means for moving said developer material from saidsump along a predetermined path to the photoconductive surface, saiddeveloper material including magnetic carrier granules and tonerparticles triboelectrically attracted to said carrier granules, anelectrically conductive member, an electrically conductive memberdisposed adjacent said magnetic transport means, means for moving saidconductive member in a transverse direction to said predetermined path,a source of electrical potential connected to said electricallyconductive member to bias said conductive member to a polarity which isthe same as the polarity of the electrostatic image, said electricallyconductive member being so located relative to said magnetic transportmeans that during movement thereof toner particles are attracted theretofrom portions of developer material on said magnetic transport meanshaving a greater quantity of toner particles dispersed therein formovement to portions of developer material on said magnetic transportmeans having lesser quantities of toner particles dispersed therein topermit attraction thereto of the toner particles on said conductivemember.
 8. The structure as recited in claim 7 wherein the movement ofsaid conductive member is reciprocal.
 9. The structure as recited inclaim 7 wherein said magnetic transport means is located to presentdeveloper to the latent image.